The present invention relates to intraocular lenses and, more particularly, to anterior chamber intraocular lenses having support haptics of filament material.
The field of intraocular lenses is fairly new, dating back to approximately 1948 when Dr. Harold Ridley of England first implanted a disc of plastic in the posterior chamber of the eye behind the iris in the former site of the crystalline lens which had been removed because of a cataractous condition. From that beginning, several major schools of lens design emerged. One of the earliest was the anterior chamber lens, such as that generally indicated as 10 in FIGS. 1 and 2. The particular design shown in simplified form as 10 in FIGS. 1 and 2 was originated by Dr. Strampelli of Italy and later made popular by Dr. Peter Choyce of England. The basic design has undergone several modifications, but is still in popular use today. Lens 10 is in the form of a rigid strip or ribbon of polymethylmethacrylate plastic 12 into which a lens portion 14 is formed at the center. Opposite ends of the strip 12 have feet 16 formed therein. The lens is placed within the anterior chamber 18 with the feet 16 disposed in the angle 20 where the iris meets the cornea 24.
There are several problems associated with rigid, platelike anterior chamber lenses. These include a lack of any longitudinal compressibility such that the diameter of the eye must be carefully measured and an attempt made to insert a lens 10 of the proper length for the specific eye. If the lens is too short, it may come free and contact the delicate endothelium lining the cornea 24. If the lens is too long, the feet 16 can press into the delicate tissue of the eye, and in particular, into the blood vessels which abound in the area, with the possibility of rupture thereof as well as a condition known as "tender eye" which can manifest itself as anything from severe pain to the constant feeling of having "something in the eye."
To prevent the iris 22 from rubbing on the strip 12, it is typical to "vault" the strip 12 as shown in side view in FIG. 2. That is, the strip 12 is not in a single plane, but curves slightly away from the iris 22 in the center. Additionally, such lenses require very careful edge polishing to prevent sharp edges which can damage delicate tissue.
It is preferred to have any implanted lens as light as possible and, as can be seen, the lens 10 of FIGS. 1 and 2 has much surplus material in the strip 12 which can be eliminated. Starting with the basic lens 10 of FIGS. 1 and 2, many designs have been created by eliminating various portions of strip 12. Lenses 26 through 34 of FIGS. 3 through 7, respectively, show some of the variations created by eliminating excess material from such a lens. Note that in all the designs, the feet 16 are integral with the lens portion 14 by virtue of a web of plastic interconnecting the two. Yet another variation (not shown) reverses the curvature of the portion containing feet 16 into a curve approximating the curve of the angle 20. Because of its similar shape, such a configuration is referred to as an "anchor" lens.
As can be imagined, lenses such as those of FIGS. 3 through 7 are even more difficult to polish than the basic shape of FIGS. 1 and 2.
From the very beginning, attempts were made to eliminate many of the foregoing problems by substituting filament material for the so-called "haptic" portion which supports the lens portion 14. Because of its ready availability and ability to be sterilized, standard suture material came to be commonly applied to such use. One of the earliest of such lenses was that of Dannheim which is indicated generally as 36 in FIG. 8. The Dannheim lens 36 had a lens body 38 having a pair of parallel bores 40 therethrough through which a continuous strand of suture material 42 was passed to form two opposed closed loops 44. It was Dr. Dannheim's belief that the lens 36 as thus constructed would adapt to varying diameters of the eye and provide a compressible lens. Unfortunately, it is typical of a looped configuration such as that of lens 36 that when the loops 44 are subjected to a longitudinal compressive force, rather than bulging outward at the side individually to foreshorten the overall length of the lens 36 in the plane of the lens body, the combined loop 44 and lens body 38 will tend to bow forward or backward in a direction normal to the surface of the lens body 38. When placed in the position shown in FIG. 2, the Dannheim lens 36 may bow back allowing the iris to rub against the lens or bow forward toward the endothelium lining the cornea 24. The smaller the diameter of the eye into which the lens was placed, the more pronounced the bowing. As a result, the lens body 38 could be placed undesirably close to the endothelium lining the cornea 24, and being effectively a spring-mounted mass, the lens body 38 might bounce against the endothelium.
Dr. Barraquer of Spain modified the Dannheim lens 36 by clipping each of the loops 44 to form a pair of opposed open loops. This eliminated the bowing problem, as he had hoped, but, unfortunately, resulted in the overall rigidity of his lens being insufficient to maintain the lens body in a stable position. After the implantation of a few lenses with unacceptable results, Dr. Barraquer ceased implantations of that design.
Wherefore, it is the object of the present invention to provide a non-rigid compressible anterior chamber lens having the benefits of a filament-type support haptic such as ease of manufacture, lightness, and smooth extruded haptics which do not require polishing, while having more desirable characteristics than prior lenses of a smiliar type.